This proposal requests funds for the purchase of a Bruker E-680 94 GHz/ 9GHz continuous-wave (cw) and pulsed Electron Paramagnetic Resonance spectrometer for use by a team of six NIH-supported investigators at Michigan State University. This instrument would provide new experimental capabilities to the major user group that would be very beneficial to their ongoing R-01 and P-01 funded research programs. The 94 GHz, or W-band, capability would allow us to address problems in metallobiochemistry that are not feasible with our current X- band (9 GHz) spectrometers. The ability to carry out W-band EPR studies in pulsed-mode may alleviate several of the problems anticipated with high frequency studies such as difficulties associated with using magnetic field modulation to detect broad absorption lines. For site- directed spin labeling (SDSL) studies, the W-band spectrometer will supply data required to obtain accurate distances between nitroxides in doubly-labeled proteins. Pulsed EPR experiments at both X- and W-band will provide more detailed information for these SDSL studies that will lead to more precise structural information. Cw and pulsed ENDOR methods will be available at both microwave frequencies. The advantages of performing ENDOR spectroscopy at high field have been pioneered by the Hoffman lab at Northwestern over the past 15 years and include enhanced sensitivity for studies of nuclei with small magnetic moments, improved spectral resolution and more precise structural information that stems from orientation-selective studies. The pulsed EPR capability at X-band will provide the major users with two- dimensional EPR/ESEEM and time domain detection techniques that will benefit several of the proposed studies. The instrument has a flexible pulse programmer, a sophisticated data acquisition system and a complement of sample probes that make it an excellent platform for the development of biological applications. Purchase of an E-680 spectrometer will shift our development efforts away from hardware building and towards solving biomedical problems.